Charged particle beam apparatus

Abstract

Improvements in a charged particle beam apparatus are contemplated and especially a column structure incorporating a superhigh vacuum evacuation system is provided which is reduced in size and weight and has high performance. In order to evacuate surrounding space of a charged particle source to superhigh vacuum, ion pumps are built in a vacuum enclosure of a column. Each ion pump includes a magnet unit 15, a yoke and an electrode, and the magnet unit per se is built in the vacuum enclosure. A charged particle beam focusing optics for focusing and deflecting a charged particle beam from the charged particle beam source is arranged in a space which is defined interiorly of the yoke. The column structure can be reduced in size and weight and a charged particle beam apparatus having high performance can be obtained.

We claim: 
     
       1. A charged particle beam apparatus comprising: a charged particle beam source for emitting a charged particle beam;   a charged particle beam focusing optics for focusing the charged particle beam from said charged particle beam source on a surface of a specimen;   a column for housing said charged particle beam source and said optics; and   an ion pump including a permanent magnet, said permanent magnet being hermetically covered with a non-magnetic electrically conductive material,   wherein said ion pump is arranged in a space inside said column and surrounding said charged particle beam focusing optics and is operated to evacuate surrounding said space of said charged particle beam source to vacuum.   
     
     
       2. A charged particle beam apparatus according to claim 1 wherein said optics is arranged interiorly of said column and substantially coaxially therewith to define said space as an annular space. 
     
     
       3. A charged particle beam apparatus according to claim 2 wherein said ion pump is arranged in said annular space, wherein said permanent magnet is a ring-shaped permanent magnet magnetized in a direction parallel to an axial direction of said column, a ring-shaped electrode having a paired component which are spaced apart from each other in the axial direction of said column to sandwich said ring-shaped permanent magnet, and a magnetic circuit arranged to surround said ring-shaped permanent magnet and said ring-shaped electrode and adapted to lead lines of magnetic force from said ring-shaped permanent magnet to form a magnetic field in a space between said ring-shaped permanent magnet and said ring-shaped electrode. 
     
     
       4. A charged particle beam apparatus according to claim 3 wherein said ring-shaped electrode having said paired component is used as a cathode electrode, said material covering said ring-shaped permanent magnet is used as an anode electrode, and said ion pump is operated by applying a high voltage between said cathode and anode electrodes. 
     
     
       5. A charged particle beam apparatus according to claim 3 wherein said magnetic circuit includes a cylindrical yoke portion arranged exteriorly of said ring-shaped permanent magnet and surrounded said charged particle beam focusing optics, ring-shaped yoke portions extending laterally outwardly of said cylindrical yoke portion to sandwich said ring-shaped electrode and said ring-shaped permanent magnet, and a circumferential wall of said column to which said ring-shaped yoke portions contact, said column being made of a dielectric material. 
     
     
       6. A charged particle beam apparatus according to claim 1 further comprising a preparatory evacuation system for preparatorily evacuating the interior space of said column, a communication opening provided between said column and said preparatory evacuation system through which the interior space of said column communicates with said preparatory evacuation system, and means for changing evacuation conductance through said communication opening. 
     
     
       7. A charged particle beam apparatus according to claim 6 further comprising a specimen chamber communicating with said column, said preparatory evacuation system being connected to said specimen chamber and said communication opening being formed in a partition wall between said specimen chamber and said column. 
     
     
       8. A charged particle beam apparatus according to claim 1 further comprising a second ion pump arranged in said space surrounding said charged particle beam focusing optics. 
     
     
       9. A charged particle beam apparatus according to claim 1 wherein said charged particle beam source is an electron beam source of field emission type. 
     
     
       10. A charged particle beam apparatus according to claim 1 wherein said charged particle beam focusing optics includes an electrostatic type objective lens for focusing said charged particle beam from said charged particle beam source on the specimen, and said electrostatic type objective lens has two lens electrodes arranged to oppose to each other, of which a first electrode is close to said charged particle source and a second electrode is close to said specimen, whereby when said charged particle beam is a negatively charged particle beam, a potential on said first electrode is kept to be positive relative to a potential on said second electrode while said charged particle beam is a positively charged particle beam, a potential on said first electrode is kept to be negative relative to a potential on said second electrode. 
     
     
       11. A charged particle beam apparatus according to claim 10 wherein said charged particle beam focusing optics further includes deflection means for scanning the charged particle beam to be irradiated on said specimen two-dimensionally on the surface thereof, and said deflection means is so constructed as to deflect and scan said charged particle beam in a space inside said charged particle beam focusing optics and in which said potential is kept at the same polarity as that of said potential on said first electrode relative to said potential on said second electrode. 
     
     
       12. A charged particle beam apparatus according to claim 1, wherein the hermetical non-magnetic electrically conductive material includes a deformable portion. 
     
     
       13. A charged particle beam apparatus according to claim 12, wherein said deformable portion is in a form of a ring shaped diaphragm groove. 
     
     
       14. A charged particle beam apparatus comprising: a charged particle beam source for emitting a charged particle beam;   a charged particle beam focusing optics for focusing the charged particle beam from said charged particle beam source on a surface of a specimen;   a column for housing said charged particle beam source and said optics; and   a first ion pump including a permanent magnet, said first ion pump being arranged in a space inside said column and surrounding said charged particle beam focusing optics and being operated to evacuate surrounding space of said charged particle beam source to vacuum;   a second ion pump arranged in said space surrounding said charged particle beam focusing optics; and   a partition wall for dividing said space into two divisional spaces, an opening formed in said partition wall through which said divisional spaces communicate with each other, and means for changing evacuation conductance through said opening, wherein said first and second ion pumps are arranged in said divisional spaces, respectively.   
     
     
       15. A charged particle beam apparatus according to claim 14, further comprising a hermetical non-magnetic electrically conductive material covers over said permanent magnet and includes a deformable portion. 
     
     
       16. A charged particle beam apparatus according to claim 15, wherein said deformable portion is in a form of a ring shaped diaphragm groove. 
     
     
       17. A charged article beam apparatus comprising: a charged particle beam source for emitting a charged particle beam;   a charged particle beam focusing optics for focusing the charged particle beam rom said charged particle beam source on a surface of a specimen;   a column for housing said charged particle beam source and said optics   a first ion pump including a permanent magnet, said first ion pump being arranged in a space inside said column and surrounding said charged particle beam focusing optics and being operated to evacuate surrounding said space of said charged particle beam source to vacuum;   a second ion pump arranged in said space and surrounding said charged particle beam focusing optic a preparatory evacuation system for preparatorily evacuating the interior space of said column, a communication opening provided between said column and said preparatory evacuation system through which the interior space of said column communicates with said preparatory evacuation system, and means for changing evacuation conductance through said communication opening;   a specimen chamber communicating with said column, said preparatory evacuation system being connected to said specimen chamber and said communication opening being formed in a first partition wall between said specimen chamber and said column;   a second partition wall for dividing said space surrounding said optics into two divisional spaces in an axial direction of said column; and   an opening formed in said second partition wall through which said divisional spaces communicate with each other; and   means for changing evacuation conductance through said opening formed in said second partition wall,   wherein said first and said second ion pumps are arranged ni said divisional spaces, respectively, one of said divisional spaces communicates with said specimen chamber through said communication opening and the other communicates with said charged particle beam source.   
     
     
       18. A charged particle beam apparatus according to claim 17, further comprising a hermetical non-magnetic electrically conductive material covers over said permanent magnet and includes a deformable portion. 
     
     
       19. A charged particle beam apparatus according to claim 18, wherein aid deformable portion is in a form of a ring shaped diaphragm groove. 
     
     
       20. A charged particle beam apparatus comprising: a charged particle beam source for emitting a charged particle beam;   a charged particle beam focusing optics for focusing the charged particle beam from said charged particle beam source on a surface of a specimen;   a casing for housing said charged particle beam source and said optics;   a space defined circumferentially interiorly between said casing and said charged particle beam focusing optic; and   an ion pump arranged in said space and operated to vacuum evacuate surrounding said space of said charged particle beam source, said ion pump including a permanent magnet covered by a hermetical non-magnetic electrically conductive material.   
     
     
       21. A charged particle beam apparatus according to claim 20, wherein said hermetical non-magnetic electrically conductive material includes a deformable portion. 
     
     
       22. A charged particle beam apparatus according to claim 21, wherein said deformable portion is in a form of a ring shaped diaphragm groove. 
     
     
       23. An ion pup used in a charged particle beam apparatus, said ion pump comprising: a ring-shaped permanent magnet;   an anode electrode disposed along said permanent magnet and hermetically covering said permanent magnet, wherein said anode electrode made of a non-magnetic electrically conductive material; and   a cathode electrode made of an active metal and sandwiched said anode electrode and said permanent magnet.   
     
     
       24. An ion pump according o claim 23 wherein each of said anode and cathode electrodes is of a ring shape. 
     
     
       25. An ion pump according to claim 23 wherein sad anode electrode substantially contacts said permanent magnet, and said cathode electrode is spaced apart from said permanent magnet, said ion pump further comprising a magnetic circuit arranged to surround said permanent magnet and said two electrodes and adapted to lead lines of magnetic force from said permanent magnet so as to generate a magnetic field which causes Penning discharge between said two electrodes. 
     
     
       26. An ion pump according to claim 25 wherein said cathode electrode includes a paired component which sandwich said anode electrode. 
     
     
       27. An ion pump as claimed in claim 23, wherein said anode electrode includes a deformable portion. 
     
     
       28. An ion pump as claimed in claim 27, wherein said deformable portion is in a form of a ring shaped diaphragm groove. 
     
     
       29. An ion pump used in a charged particle beam apparatus comprising: a ring-shaped permanent magnet arranged in a column coaxially with focusing optics for a charged particle beam;   an anode electrode disposed along said permanent magnet and hermetically covering said permanent magnet, wherein said anode electrode made of a non-magnetic electrically conductive material; and   a cathode electrode made of an active metal and sandwiched said anode electrode and said permanent magnet.   
     
     
       30. An ion pump according to claim 29 wherein each of said anode and cathode electrodes is of a ring shape. 
     
     
       31. An ion pump according to claim 29 wherein said anode electrode substantially contacts said permanent magnet, and said cathode electrode is spaced apart from said permanent magnet, said ion pump further comprising a magnetic circuit arranged to surround said permanent magnet and said two electrodes and adapted to lead lines of magnetic force from said permanent magnet so as to generate a magnetic field which causes Penning discharge between said two electrodes. 
     
     
       32. An ion pump according to claim 31 wherein said cathode electrode includes a paired component which sandwich said anode electrode. 
     
     
       33. An ion pump as claimed in claim 29, wherein said anode electrode includes a deformable portion. 
     
     
       34. An ion pump as claimed in claim 33, wherein said deformable portion is in a form of a ring shaped diaphragm groove. 
     
     
       35. A method of pumping down a charged particle beam apparatus, said apparatus comprising: a charged particle beam source for emitting a charged particle beam;   a charged particle beam focusing optics for focusing the charged particle beam from said charged particle beam source on a surface of a specimen;   a column for housing said charged particle beam source and said optics; and   an ion pump means including a permanent magnet, said permanent magnet being hermetically covered with a non-magnetic electrically conductive material,   wherein said ion pump means is arranged in a space inside said column and surrounding said charged particle beam focusing optics and is operated to evacuate surrounding space of said charged particle beam source to vacuum;   a preparatory evacuation system for preparatorily evacuating the interior space of said column, a communication opening provided between said column and said preparatory evacuation system through which the interior space of said column communicates with said preparatory evacuation system, and means for changing evacuation conductance through said communication opening;   a specimen chamber communicating with said column, said preparatory evacuation system being connected to said specimen chamber and said communication opening being formed in a first partition wall between said specimen chamber and said column;   a second partition wall for dividing said space surrounding said optics into two divisional spaces in an axial direction of said column;   an opening formed in said second partition wall through which said divisional spaces communicate with each other; and   means for changing evacuation conductance through said opening formed in said second partition wall,   wherein said ion pump means comprises a plurality of ion pumps arranged in said divisional spaces, respectively, one of said divisional spaces communicates with said specimen chamber through said communication opening and the other communicates with said charged particle beam source;   said method comprising the steps of:   opening said communication opening and said opening and evacuating the interior of said column to a condition of a first vacuum by means of said preparatory evacuation system;   closing said communication opening or adjusting conductance thereof and operating at least one of said ion pumps to evacuate the interior of said column to a condition of a second vacuum in which a vacuum degree is higher than in said first vacuum condition; and   closing said opening or adjusting conductance thereof and operating said ion pump arranged in said divisional space in communication with said charged particle beam source to evacuate surrounding space of said charged particle beam source to a condition of a third vacuum in which a vacuum degree is higher than in said second vacuum condition.   
     
     
       36. A charged particle beam apparatus comprising: a charged particle beam source for emitting a charged particle beam;   a charged particle beam focusing optics for focusing the charged particle beam from said charged particle beam source on a surface of a specimen;   a column for housing said charged particle beam source and said optics; and   an ion pump including a permanent magnet, said permanent magnet being hermetically covered with a non-magnetic electrically conductive material,   wherein said ion pump is arranged ni a space inside sa column and is operated to evacuate surrounding said space of sad charged particle beam source to a vacuum.   
     
     
       37. A charged particle beam apparatus according to claim 36, further comprising a wall for separating said space into a space surrounding the charged particle beam source and another space surrounding said optics containing said ion pump, said wall being provided with an opening through which the space containing said ion pump and the surrounding space of the charged particle beam source communicates, the opening being arranged at the substantially peripheral portion of the wall and being spaced apart from the source. 
     
     
       38. A charged particle beam apparatus comprising a charged particle beam source for emitting a charged particle beam;   a charged particle beam focusing optics for focusing the charged particle beam from said charged particle beam source on a surface of a specimen;   a casing for housing said charged particle beam source and said optics;   a space defined circumferentially interiorly between said casing and said optics;   a wall for separating said space to form a space surrounding the charged particle beam source and another space surrounding said optics;   an opening being arranged at the substantially peripheral portion of the wall and being spaced apart from the source; and   an ion pump arranged in said space surrounding said optics and operated to vacuum said surrounding space of said charged particle beam source through said opening.